Nye, Monica D.

Abstract Crosstalk between signaling pathways is crucial to the initiation, progression and maintenance of the transformed phenotype. Therefore, characterization of these signaling interactions is fundamental for the understanding of the complex and varied network of events that leads to the development and spread of tumors. The Hedgehog (HH)-GLI pathway, an important carcinogenic cascade, is required for the growth and survival of tumors of diverse origin. Recent reports, mainly from animal models, suggest that key signaling interactions are required by HH-GLI signaling to modulate cancer-associated cellular functions. However, the molecular mechanisms underlying this phenomenon in cancer and non-cancer cells remain elusive. Our preliminary data show a crosstalk between the HH-GLI axis and TGF-beta pathway, a well-characterized tumor suppressor/oncogenic signaling pathway. Luciferase reporter and expression assays in combination with genetic and pharmacological manipulations of the TGFbeta pathway show that this cascade is able to activate GLI transcriptional activity, even in the absence of an active HH signaling. The TGFbeta pathway is required to maintain active GLI transcriptional complexes at GLI target genes. Further analysis of this molecular interaction suggests that TGFbeta pathway-mediated activation of GLI transcription factors requires an intact SMAD4, thus suggesting a potential mechanism mediating this functional interaction. The knowledge derived from this study provides both mechanistic insight into the contribution of this HH-GLI/TGF-beta pathway interaction to carcinogenesis and could serve as a foundation for development of new therapeutic approaches for tumors with active HH-GLI and TGF cascades. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3917.

Abstract Heat shock protein 90 (HSP90), which regulates the functions of multiple oncogenic signaling pathways, has emerged as a novel anticancer therapeutic target, and multiple small-molecule HSP90 inhibitors are now in clinical trials. Although the effects of HSP90 inhibitors on oncogenic signaling pathways have been extensively studied, the effects of these agents on tumor suppressor signaling pathways are currently unknown. Here, we have examined how HSP90 inhibitors affect LATS1 and the related protein LATS2, two kinases that relay antiproliferative signals in the Hippo tumor suppressor pathway. Both LATS1 and LATS2 were depleted from cells treated with the HSP90 inhibitors 17-allylamino-17-demethoxygeldanamycin (17-AAG), radicicol, and PU-H71. Moreover, these kinases interacted with HSP90, and LATS1 isolated from 17-AAG–treated cells had reduced catalytic activity, thus showing that the kinase is a bona fide HSP90 client. Importantly, LATS1 signaling was disrupted by 17-AAG in tumor cell lines in vitro and clinical ovarian cancers in vivo as shown by reduced levels of LATS1 and decreased phosphorylation of the LATS substrate YAP, an oncoprotein transcriptional coactivator that regulates genes involved in cell and tissue growth, including the CTGF gene. Consistent with the reduced YAP phosphorylation, there were increased levels of CTGF, a secreted protein that is implicated in tumor proliferation, metastasis, and angiogenesis. Taken together, these results identify LATS1 and LATS2 as novel HSP90 clients and show that HSP90 inhibitors can disrupt the LATS tumor suppressor pathway in human cancer cells. Cancer Res; 70(21); 8642–50. ©2010 AACR.